Hi and thanks for the query, A careful clinical evaluation is required to come out with the difference. A past history of visiting a tick infected area, or if you live in a zine where ticks and lyme disease is frequent, kit could be. The rash however in lyme disease is large erytematous reddish and very characteristic and usually accompanied by joint pain. In lupus, other symptoms like a non reddish discoid rash is usually seen. Making the difference with a clinical evaluation is sufficient. Blood tests like the Anti nuclear antibody test Anti Sm antibodies are generally positive in lupus but absent in lyme. Active search for a thick locus and lyme antibodies are widely available in search of the antibodies for Borrelia, which causes lyme disease. I suggest you book an appointment with a dermatologist. Thanks and best regards, Bain LE, MD.